Cyber Monday online sales grew 9 percent in the first 12 hours compared to the same period last year, IBM's data analytics division reported. Twenty-three percent of purchases were made with mobile phones, a 29 percent increase from last year.

"There's been a giant rise in the number of people who use mobile devices" to shop online, said Jay Henderson, director of IBM Smarter Commerce. "Mobile is the new Thanksgiving tradition."

During the Thanksgiving weekend, online sales grew 17 percent from last year, and a third of sales were made on mobiles, IBM said. In 2010, only 6.5 percent of sales were made on mobile devices.

Still, average orders were flat at $135.51, IBM said. Shoppers are twice as likely to buy on a tablet than a mobile phone, and spend a bit more shopping on desktop computers than cell phones. The average order during the weekend from a desktop computer was $128.60, compared to $112.81 on a phone, IBM said.

Americans are expected to spend as much as $2.5 billion on Cyber Monday.

Adobe reported online sales from midnight to 10 a.m. grew 17 percent to $719 million compared to last year, driven by more mobile shopping than expected and lower prices earlier in the morning. Adobe predicted sales would slow throughout the day, bringing the day’s sales closer to the forecasted 15 percent growth.